1. Field of the Invention
This invention relates generally to power conversion and particularly to a multiple-input DC-DC converter which is capable of power diversification among different energy sources with different voltage-current characteristics, while achieving bidirectional operation and a positive voltage output.
2. Discussion of Related Art
DC-DC converters are used to convert a source of direct current (DC) from one voltage level to another. Multiple-input converters have the capability to combine the advantages of different energy sources, such as photovoltaic cells, fuel cells, wind power devices, batteries, ultracapacitors and other renewable energy sources, with different voltage and current characteristics to provide power and for optimal energy/economic use while increasing the reliability of a system. Multiple-input converters are useful in many systems/applications including grid connected integrated hybrid generation systems, fuel cells, micro grid-based telecom power systems, uninterruptible power supplies, and electric or hybrid electric vehicles.
Known multiple-input converters are useful for combining several energy sources, with varied power capacity and/or voltage levels, to obtain a regulated output voltage. A common limitation of some known multiple input converters is that only one input power source is allowed to transfer energy into an output at a time to prevent power coupling effects.
Other known converters overcome the above limitation by utilizing a transformer with separate windings for each input. This type converter can also accommodate multiple-outputs by using multiple secondary windings. In this way, any input can provide energy to any output, and there is electrical isolation among all inputs and outputs. However, this type of converter requires a large transformer core to accommodate all of these windings, making the design big and costly.
Current-fed multiple-input converters can transfer energy from different power sources into a load through a multi-winding transformer, however, these converters require a large number of power switches and a complicated gate drive circuit and controller. Thus, these converters have a relatively high cost and a large number of parts.
Another type of multiple-input converter has a negatively referenced output and is unidirectional. The output could be reversed by utilizing a transformer, which adds to the cost and size of the topology. In order to make this type of converter bidirectional, it is expected that an additional converter from the output to each input would be required.
There is a need for a multiple-input converter which is capable of combining different energy sources, with bidirectional operation and while achieving a low parts number.